1. Field of the Invention
The present invention relates to a method for manufacturing a glass fiber having a polygonal cross section.
2. Description of the Prior Art
Recently, the demand for glass parts has increased in accordance with the development of electronics, and various types of glass have been developed from the point of view of shape as well as composition and property. Typical shapes of such glass are of plate, powder, tube, capillary, disk, fiber, and the like. The present invention relates to a method for manufacturing a glass fiber.
A prior art method will be described hereinbelow, using a sealing glass for the application to a gap of a magnetic head as one example. FIG. 3 shows a representative manufacturing process of a magnetic head for a video tape recorder.
In FIG. 3, material of a tip 45 for the magnetic head is cut from a ferrite ingot 44 in step (a), and the surface of the material is ground so as to make a bar suitable in size in step (b). Next, grooves 46 for placing reinforcing glass are made by a track processing in step (c), and glass 47 is molded into the grooves in step (d). Then, the excessive glass is ground, and the surface of a gap 49 is polished with a groove for a coil being made in step (e). Thereafter, glass for the gaps is sputtered, and the two bars are adhered to each other, so gaps 50 are formed in step (f). Then, the adhered bar is cut to make tips in step (g), and the sides of the tip are polished to make a tip 52 having a suitable size in step (h). Next, the tip 52 is adhered to a base 53 in step (i), a tape traveling surface 54 is polished in step (j), and a magnetic head 55 is completed with wire (not shown) being wound in step (k).
As shown in FIG. 4, a ferrite 12 is adhered to the completed magnetic head with glass for adhesion 13.
In the above-mentioned glass mold process of FIG. 3 step (c), generally, a fiber glass is used as the mold glass. Moreover, recently, a fiber glass having a quadrangular cross section is used more than a fiber having an orbicular cross section. This is because, as shown in FIG. 5, in the case of the orbicular fiber, a back grooved section 58 must be provided at the opposite side of the grooves by the track processing of a ferrite bar 57, and a jig 59 for giving inclination must be used in order to prevent the orbicular fiber 56 from falling down. Therefore, in the case of the quadrangular fiber, it is unnecessary to consider the above-mentioned two matters as shown in FIG. 6, and a simple base 9 can be used. Although the fiber shown in FIG. 6 has a quadrangular cross section, a fiber having a triangular cross section may also be used.
There are two conventional and representative methods by which a glass fiber having a quadrangular or a triangular cross section is formed. One of them is a method, as shown in FIG. 7, in which a block of glass 38 is cut by a diamond cutter and the like, so as to make a plate 39 and the plate 39 is cut to form a fiber 40 having the desirable size. However, in this conventional method for producing a glass fiber, there are problems which will be described hereinbelow. When cutting the glass block, it is necessary to pour water onto the cutting portions so that the cutting portions are cooled and the cut powders are cleared away. At this time, the water reacts with the glass because a large amount of heat is generated during the cutting and the temperature rises. As a result, the glass in the vicinity of the cutting portions is liable to change in quality. Moreover, it is difficult to make a flat surface of the cutting portions due to chatter vibrations of the glass cutting. Therefore, the resulting surface has an unevenness, so that the surface of the glass is rough and the glass is cloudy. When the above-mentioned step (d) is carried out for the production of the magnetic head using this fiber, the air existing in the concave portions of the unevenness of the surface is enclosed into the glass, so that the air remains in the glass as bubbles. The glass having bubbles causes recording and reproducing efficiency to attenuate at the head, leads to the flaw in the tape, and causes the tip to crack.
The other method, as shown in FIG. 8, is that first, a glass block 41 is cut so as to obtain a small block 42 whose thickness is about ten times larger than the desired thickness by using a diamond cutter and the like. The small block 42 is then heated and drawn to make a glass fiber 43 having a polygonal cross section. However, even in this method, it is indispensable to cut the glass block in order to make a small block. Therefore, the glass in the vicinity of the cutting portions inevitably changes in quality.
The surfaces of the glass fibers obtained by the conventional methods shown in FIGS. 7 and 8 are analyzed by using an ESCA, which is a kind of an electron spectroscopy, which reveals that on the surfaces, modified layers caused by the processing has a composition that is different from that of the internal portions. For example, when a ratio of lead having a peak strength of 4f.sub.7/2 to silicon having a peak strength of 2P (lead/silicon) is examined by the ESCA, the ratio on the surfaces of the glass fibers is 2, and that in the internal portions is 10. In this way, when water is used while the glass is being cut, lead is eluted onto the surface of the glass and the amount of lead on the surface becomes 1/5 of that of the internal portion, thereby forming a modified layer caused by processing on the surface of the glass.
A method for producing a glass fiber having a polygonal cross section without cutting a glass block has been proposed. For example, as shown in FIG. 9, molten glass 31 is poured into a metal mold 30 having a polygonal cross section so as to form a base bar 32, and the base bar 32 is heated and drawn into a heating furnace, whereby a glass fiber 33 having a polygonal cross section can be produced. In order to mass-produce glass fibers by using this method, first, a plurality of base bars 32 are provided, one base bar is drawn, this base bar is removed from a heating furnace and another base bar must be placed in the heating furnace. Therefore, there arises a problem in that production efficiency is unsatisfactory.
Furthermore, U.S. Pat. No. 4,885,020 discloses a method for producing a glass fiber having a polygonal cross section. According to this method, as shown in FIG. 10a, the molten glass 31 accommodated in a crucible is pulled up, thereby molding the glass into a fiber 34 having an orbicular cross section. After that, the fiber having an orbicular cross section is passed through a polygonal slit 35 provided at a twin roller as shown in FIG. 10b, whereby a fiber 37 having a polygonal cross section is produced. In this method, when the glass in the crucible is decreased in amount, the molding of the glass fiber is stopped, molten glass is supplied into the crucible, and the crucible must be heated so that the supplied glass and the glass which has been stored in the crucible become uniform. After that, the crucible must be sufficiently cooled until the molten glass has sufficient viscosity to be pulled up. In this way, even in this method, there are problems in that the production efficiency is unsatisfactory, and fibers having a polygonal cross section cannot be successively produced.